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The DC transport properties of and the radio-frequency (RF) wave absorption (at 1.33 MHz) in a ceramic sample of La[SUB0.5]Sr[SUB0.5]CoO[SUB3 - δ] are measured. The Curie temperature T[SUBc] of the sample is about 250 K. A giant negative magnetoabsorption effect is found. In the vicinity of T[SUBc], the absolute value of the magnetoabsorption is about 38% in the rather low magnetic field 2.1 kOe. This differs drastically from the measured DC magnetoresistance (MR) δ(H) = [R(0) - R(H)]/R(0) which is a mere 0.26% near T[SUBc] in the same field and increases to about 2.15% in H = 20 kOe. The phenomenon can be understood taking into account that the magnetoabsorption is determined by influence of magnetic field on the conductivity and the magnetic permeability, while the MR is determined solely by the former. The magnetoabsorption effect can be used to develop RF devices controlled by magnetic field and temperature. [ABSTRACT FROM AUTHOR]

Thermodynamic characteristics of the perovskite-like compound La2/3Ba1/3MnO3, exhibiting a structural phase transformation of the martensitic type with a characteristic temperature Ts≈200 K, are studied in the temperature range 2–340 K. Step-like hysteretic temperature behavior of the effective heat capacity is revealed at 150–250 K and attributed to the discrete kinetics and a latent heat of the martensitic transformation. The magnetic subsystem is found to exhibit a magnetic glass state below 220 K and temperature hysteresis of the magnetic susceptibility clearly pronounced in the 40–100 K and 180–230 K regions. The Debye and Einstein temperatures, θD=230 K and θE=500 K, respectively, derived from the experimental Debye–Waller factors for the La/Ba, Mn, and O sublattices, are used to refine contributions from the structural and magnetic transformations to the heat capacity and to reveal thermodynamically nonequilibrium states. [ABSTRACT FROM AUTHOR]

The temperature dependences of the long diagonals dMn–O of the MnO6 octahedron and the magnetic susceptibility χ of Nd2/3Ca1/3MnO3 in the temperature interval 100–290 K are investigated. The functions dMn–O(T) and χ(T) are found to have anomalies in the charge-ordering range (Tco≈212 K). The sharp decrease of the diagonal dMn–O2s agrees with phase-transition notions, according to which the spatial modulation of the charge density is due to the modulation of the Mn–Mn bond lengths. The most likely driving forces of the transition are the Peierls lattice instability and Jahn–Teller stability of the MnO6 octahedron at the Mn3+ ions. The hysteresis of the temperature dependence χ(T) in the paramagnetic region shows indirectly that structural phase separation occurs together with the transition. The parameters of the function χ(T) indicate that ferromagnetic clusters consisting of one, two, or three ion pairs Mn3+–Mn4+ form in the system in the temperature intervals 274 K≼T≼290 K, 224 K≼T≼252 K, and 130 K≼T≼198 K, respectively. [ABSTRACT FROM AUTHOR]

The transformation of the magnetic absorption spectra of a narrow-band ferromagnetic conductor containing local f and quasilocal d magnetic moments under conditions of weak spin–lattice coupling and spatial randomization of the g factors of the quasilocal and local spin subsystems is investigated. It is shown that randomization of the g factors (e.g., as a result of the introduction of an impurity) leads mainly to the “opening” (i.e., to the appearance in the magnetic absorption spectrum) of acoustic and optical magnon bands formed in the system while not affecting the position and shape of the narrow magnetic resonance lines comprising the spectrum of the impurity-free crystal. The effects of spin–lattice coupling, besides the “opening” of the phonon and magnon bands, lead to a shift and a temperature smearing of the narrow resonance lines. The relative corrections to the effective magnon masses generated by the spin–lattice coupling in a 4f–5d metal amount to ∼2×10-4 for an acoustic mode and to ∼4×10-4 for an optical mode. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In narrow-band ferromagnetic conductors containing local f and quasilocal d magnetic moments the interatomic spin correlations created by the confined effects of the intra-atomic interactions of the quasilocal electrons and their intersite hops are playing a role in the formation of the magnetic resonance spectra. This role is examined, and the transformation of the spectra of the transverse dynamic magnetic susceptibility under conditions of weak spin-lattice coupling and spatial randomization of the g factors of the quasilocal and local spin subsystems is investigated. A calculation done by the method of two-time retarded Green's functions shows that the interaction of the d and f electrons leads to an effective renormalization of the g factors of both magnetic subsystems, and at zero temperature the spin-lattice coupling lowers the frequency of the inhomogeneous magnetic resonance and causes threshold damping of acoustic and optical magnons. [ABSTRACT FROM AUTHOR]

The static magnetization M[sub N] and dynamic magnetic susceptibility χ[sub ac] of polycrystalline manganite La[sub 0.66]Ba[sub 0.34]MnO[sub 3] are investigated in the temperature region 5 K

The magnetization M(T) and electrical resistivity ρ(T) of a La[sub 2/3]Ca[sub 1/3]MnO[sub 3] film have been studied in the temperature range 5 K≤T≤320 K in the magnetic field intervals 10 Oe≤H ≤400 Oe and 0≤H≤50 kOe, respectively. It is found that the M(T)/M(0) value is larger than that predicted by the conventional molecular field model below the Curie point T=267 K, and that the ln ρ(T) dependence is close to linear in the temperature range 80 K< T< 200 K (accordingly, ∂ ln ρ/∂T is constant in this region). A model of the electrical conductivity and magnetoresistivity of the system describing qualitatively the experimental results is proposed (the Am r model). The model includes a thermally activated (with characteristic energy Δ) mechanism of conductivity, dependence of the concentration and the effective mass (m) of the itinerant charge carriers on the magnetization, as well as scattering (with characteristic time τ) of the charge carriers by static breakings of the translational symmetry, thermal fluctuations of the magnetic order, and phonons. [ABSTRACT FROM AUTHOR]

Magnetization of La0.66Ba0.34MnO3 and its temperature behavior under a uniaxial pressure of 0.1 kbar are measured between 5 and 270 K in magnetic fields 0